The present invention relates to a method and a device for digital control of electrical consumers in a model railway, in which: the consumers are provided with energy by means of a square wave voltage applied to the track, and are controlled by modulation of this square wave voltage in accordance with a digital control information, and a consumer having received a control information intended for the consumer applies a return signal to the track. The modulation of this combined control and power supply voltage, also referred to as track signal, is preferably a pulse width and/or frequency modulation. To this end, a control device connected to the track is provided, which modulates the square wave voltage in accordance with digital control information and, in this manner, not only supplies the consumers with energy but also controls them as well. In the consumer there are provided a receiver for receiving the control information and, in addition thereto, a return signal generator for generating a return signal returned via the track. The return signal generator is preferably integrated in the receiver. In other words, the invention relates to a method and a device which make bi-directional data transmission possible in digitally controlled model railways.
The term square wave voltage here denotes a voltage having a rectangular wave form relative to the basic frequency of this voltage, i.e. a voltage having an approximately rectangular voltage wave shape. Basically, the present invention may be applied to other voltage shapes as well, for example a voltage having a sinusoidal gradient; however, modulation with digital control information and hence demodulation then become more complicated. Furthermore, the NMRA standards mentioned further below require a rectangular voltage gradient.
Such a control including return signal generation has been known from DE 100 11 978 A1 and had been developed to meet increasing demands for returning information from consumers on the model railway to the control device or to indicating and operating components of the model railway. In the electrical consumers, receivers for digital control information are provided. Such consumers may both be mobile consumers (locomotives, as a rule) and stationary consumers (track switch operation mechanisms, for example) as has been described in detail in DE 100 11 978 A1. The returned information may include a locomotive address, an actual speed value, a motor temperature, etc. When assigning this information data to a corresponding track section where they have been received by the consumer located on the section, an easy localization of mobile consumers by means of a central control device provided for a plurality of track sections becomes possible. If the central control then has a return signal or return message, for example in form of a command acknowledgement, the control functions for the model railway can be optimized and a comfortable and safe operation is possible.
A solution shown in DE 100 11 978 A1 for implementing return signals was designed such that existing standards for control of digital model railways are not violated and the performance of control components is not impaired. The standard on which both DE 100 11978 A1 and the present application are based corresponds to NMRA DCC Electrical Standard and NMRA DCC Communication Standard for the transmission of data on the track, or track sections, respectively, of a model railway system.
In DE 100 11 978 A1, the supply voltage supplied to the track is a square wave voltage which, depending on the digital control information, is frequency and/or pulse length modulated. The method of DE 100 11 978 A1 is characterized in that a consumer supplies the track with a return signal of a frequency higher than the frequency of the modulated square wave voltage. This return signal is, under synchronization on the square wave voltage, detected in sections of the square wave voltage which are free of signal edges. In this method, the square wave voltage is superimposed by the higher frequency return signal. Detection of the return signal occurs in signal edge free voltage sections of constant digital level, preferably longer signal edge free sections resulting from the modulation, such as the second signal half of a zero information bit when using the NMRA DCC Electrical Standard and the NMRA DCC Communication Standard.
This process, however, requires means for generating a transmitting or carrier frequency, and moreover means provided for recovering the returned signal from noise spectrum on the track which always exists. When, as usual, a plurality of track sections insulated from each other exist, elaborate filters for avoiding cross talk from signal returning consumers located at other track sections are required. The individual bits of the return signal are timely synchronized to the track signal. This leads to a limitation of the amount and rate of transmission. Per track bit, one return bit can only be transmitted. There exists a possibility of a negative influence on the return signal transmission by already-existing digital components on the model railway which do not comply with the requirements for the transmission of return data and which attenuate the return signal too much.
In a control system according to U.S. Pat. No. 6,220,552 B1, interference pulses from various sources are removed, under correspondingly high technical efforts in order to detect the presence of individual pulse sequences. Detection and evaluation of the pulse sequences, inter alia by means of determining their polarities, are elaborate and time consuming so that rapid data transfer is not possible. The signal line impedances of a wired model railway described in that patent are stated to allow a detector to receive the signal to be detected both directly from the track and from the central control. Hence, an unambiguous assignment of the signal polarity or direction required to detect the pulse sequences is possible only with increased elaboration.
The elaboration for avoiding cross-talk is correspondingly large. Regarding the cross-talk of individual bits to the track signal, the above-referenced limitation applies in the present case as well.
In an earlier not pre-published application DE 101 03 202 assigned to the Assignee of the present application, a return transmission for localizing a locomotive on a track section of a model railway having a plurality of separated track sections is described. In that case again, a localizing return signal of higher frequency than the frequency of the square wave voltage is superposed to the square wave voltage while synchronizing it thereto. A problem comes up similar to that described in DE 100 11 978 A1.